1. Field of the Invention
This invention relates to artificial lift of fluids and gas from subsurface reservoirs. More specifically it relates to performance optimization of fluid and gas artificial recovery from subsurface formations, using a surface mounted reciprocating hydraulic pump, controlled by a computer and a set of specific algorithms.
2. Description of Prior Art
Flow into a petroleum well bore depends upon the characteristics of the reservoir formation and its fluids. It also depends upon the well bore conditions while it is producing. Petroleum well characteristics undergo changes during the operating life of the well, some of which the well operator can manage directly while others can be hardly controlled. After an initial phase of free flowing production and as reservoir pressure is declining, there is a need to employ artificial means to continue to recover fluid. A variety of techniques and equipment have been developed over time to extract oil and gas from subsurface formations.
A mainstream method to recover fluid from the ground is rod lifting. This method features a subsurface downhole pump immersed in a casing tube and attached via a rod string to a surface mounted reciprocating mechanism. The reciprocating mechanism, hereinafter defined as the surface pump, is lifting a column of fluid and gas in each stroking cycle. The most conventional and recognized rod lifting pump is the “horse head” beam pump.
The operating characteristics of the lifting system determine its economic efficiency, namely its production capacity and its operating costs. Pumping speed is a critical operating parameter in determining the overall lifting system efficiency. Ideal pumping occurs when the inflow rate of the well equals the pumping rate, with the downhole pump being fully submerged in fluid, allowing complete filling of the downhole pump on every stroke. In other words, ideal pumping occurs when the fluid level in the well bore is maintained close above the top of the downhole pump during operation.
Optimal speed on the up stroke can be defined as the maximum speed that will not cause (a) pumped off condition of the well, or (b) overstressing of the rod string and its associated structural components. Maximum speed on the upstroke also minimizes the leakage of produced oil, thereby increasing production efficiency.
Optimal speed on the down stroke can be defined as the maximum speed which will not cause floating of the polished rod. Floating of the polished rod on the down stroke can cause separation of the polished rod from the carrier bar, leading to uncontrolled impact loads between them when they come back together on the up stroke. Acceleration and deceleration of the fluid column and the moving parts of the lifting system during motion and specifically during turnaround determine the magnitude of dynamic loads and resultant stresses on the structural parts of the pump.
Operation at speeds lower than the optimal speed causes loss of production. Operation at higher than the optimal speed causes pumped off conditions, with partial fillage of the downhole pump. Operation in pumped off conditions is causing pounding loads between the pumping equipment and the fluid, resulting in overstressing of structural parts, their premature damage, high maintenance costs and a shortened life of the pumping equipment.
There is a need to develop a mechanism which can control closely the position, velocity and acceleration of a rod lifting system at any point in real time.
Prior art has been utilizing open loop control, fixed set point control or simple closed loop feedback control to manage performance of typical oil lifting machines such as the traditional beam pump. Traditional beam pumps operate on the basis of a four bar linkage geometry. In a typical beam pump embodiment the circular motion of a crank arm, driven by an electric motor or a combustion engine, is converted into reciprocating motion of the polished rod. The position, velocity and acceleration sinusoidal characteristics of the polished rod are very complicated and are, therefore, hard to control by the crank arm drive in real time. The difficulty to control these parameters is greatly compounded by typical large dynamic inertias of the moving parts of the beam pump and its balancing weights.
Present technology features a great variety of sensor readings and control devices that enable to monitor numerous well data. However, operator's intervention, either at the factory or in the field, has always been required to adjust parameter settings, in response to varying operating conditions and in order to improve performance and production efficiencies of the lifting system.
Adjustment of the stroke length of a beam pump is an example of typical need for operator's intervention when changing pumping parameters. A beam pump stroke is adjusted by physically removing and replacing its arms length. Another example is speed adjustment methods in reaction to varying load conditions. Up stroke and down stroke conditions vary during operation, requiring adjustments of the upstroke speed, the down stroke speed or both. Present technology requires operator's intervention to adjust these speeds. Moreover, most present technologies do not enable to set different up and down speeds, as optimization of pumping performance often requires.
In extreme cases, like rod parting, safe stoppage is required. Most systems are not smart enough to “safe land” the system softly without causing major damage, costly maintenance and wasted production down time.
Oil fields are characterized by being located most often in remote and hard to access sites. There is a need to improve the ability to monitor and manage oil pump performance in order to improve its productivity and react timely to hazardous conditions without the need to employ physical intervention of an operator.
The following ten issued patents and published patent applications are the closest prior art known to the present inventor which relate to the field of the present invention:    1. U.S. Pat. No. 5,193,985 issued to Nelson Escue et al. and assigned to UniFlo OilCorp., Ltd. on Mar. 16, 1993 for “Pump Control System For A Down Hole Motor-Pump Assembly And Method of Using Same” (hereafter the “Escue patent”);    2. U.S. Pat. No. 5,941,305 issued to William R. Thrasher et al. and assigned to Patton Enterprises, Inc. on Aug. 24, 1999 for “Real-Time Pump Optimization System” (hereafter the “'305 Thrasher Patent”);    3. U.S. Pat. No. 6,041,856 issued to William B. Thrasher et al. and assigned to Patton Enterprises, Inc. on Mar. 28, 2000 for “Real-Time Optimization System” (hereafter the “'856 Thrasher Patent”);    4. U.S. Pat. No. 6,213,722 issued to Davor Jack Raos on Apr. 10, 2001 for “Sucker Rod Actuating Device” (hereafter the “Raos Patent”);    5. United States Published Patent Application No. 2004/0149436 to Michael L. Sheldon on Aug. 5, 2004 for “System And Method For Automating Or Metering Fluid Recovered At A Well” (hereafter the “'0149436 Sheldon Published Patent Application”);    6. United States Published Patent Application No. 2006/0032533 to Michael L. Sheldon on Feb. 16, 2006 for “System And Method For Automating Or Metering Fluid Recovered At A Well” (hereafter the “'0032533 Sheldon Published Patent Application”);    7. United States Published Patent Application No. 2009/0055029 to Alan L. Roberson et al. and assigned to Lufkin Industries, Inc. on Feb. 26, 2009 for “Real-Time Onsite Internet Communication With Well Manager For Constant Well Optimization” (hereafter the “Roberson Published patent application);    8. UK Patent Application No. GB 2 344 910 to Paulo S. Tubel et al. and assigned to Baker Hughes Incorporated on Jun. 21, 2000 for “Method for Remote Control Of Wellbore And Devices” (hereafter the “'910 Tubel UK Patent Application);    9. UK Patent Application No. GB 2 344 911 to Paulo S. Tubel et al. and assigned to Baker Hughes Incorporated on Jun. 21, 2000 for “Method of Remote Control of Wellbore And Devices” (hereafter the “'911 Tubel UK Patent Application”);    10. PCT Application No. WO 01/16487 to Ying Li on Mar. 8, 2001 for “A Pumping Unit” (hereafter the “Li PCT Application).
The Escue patent discloses a control system for monitoring and controlling the operation of a downhole linear DC motor-pump assembly. The system includes a surface monitoring station that is in radio communication with a plurality of remote downhole motor-pump assemblies. Each motor-pump assembly has a surface motor controller and a downhole motor-pump cartridge unit in a stationary position for pumping purposes. The motor-pump cartridge unit may be raised or lowered by a control cable within the production tubing for helping to facilitate the repair or replacement of the motor-pump cartridge unit. This does not disclose continuously monitoring the pump and also does not use a hydraulic piston but instead discloses use of a DC motor pump assembly.
The Raos patent discloses a method for pumping a fluid utilizing a sucker rod assembly and an electric linear motor and counterbalance which includes positioning the sucker rod pump assembly such that the pump contacts a fluid reservoir, positioning a linear control motor such that the axis of operation is substantially the same as the axis of movement of the sucker rod, attaching the top end of the sucker rod to the armature of the linear motor such that when operable, the armature directly drives the rod, providing a counterbalance positioned such that it alleviates the load imposed on the linear motor by the sucker rod and the column of fluid to be pumped, and operating the motor such that the pump acquires fluid on its down stroke and transports fluid on its up stroke. The patent discloses the concept of hydraulic pumping means and a feedback loop where pumping parameters are monitored by computer.
The '0149436 Sheldon Published Patent Application discloses a system and method for automating or metering fluid recovered at a well. The patent discloses:
“In the preferred embodiment, the control module 16 consists of a microprocessor-based controller 20 that provides the functions required for a variety of field automation applications that would enable local or remote monitoring, measurement and data archival, and control of the oil recovery device. For example, a Programmable Logic Controller (commonly known as PLC) could be used. One relatively inexpensive and currently available PLC is provided by Unitronics Industrial Automations Systems. Unitronics' PLC has sufficient processing ability, number of timers, memory, to control an oil recovery device and has the ability to provide bi-directional communications. Other controllers are also available and could be adapted for use in the present application. Such devices also include sufficient process inputs and outputs (I/Os) 22 for connecting the controller to the various electrical components of the oil recovery device. The benefit of the multiple I/Os is that it enables the module to connect to various devices for collecting measured and sensed data for controlling or diagnosing the operation of the oil recover system. In other words, the control module is used to automate the recovery system and allow for remote communication and control of the operation of the recovery system. For example the extractor unit uses a spool assembly to raise and lower a canister to collect oil in the well. Preferably a proximity sensor is used to monitor the rotation of the spool to measure and control the depth of the canister. Further, the limit switches, used to detect when the canister has been seated properly into the discharge head, are detected by the control module and are used to control both the motor and the compressor to pump the oil out of the canister. Timers within the control module (commonly provided with most PLCs) can also control the various aspects of the cycle, i.e., when and how long to run the compressor, how long to keep the canister at the top of the well before sending it down the well for another load, how long to keep the canister at a preselected depth to collect oil, etc. The control module also has the ability to tune the recovery process for optimal recovery as will be discussed below.”
The '0032533 Sheldon Published Patent Application is a division of the above published patent application and has been abandoned. It has a similar concept as described above.
The Roberson Published patent application discloses:
“An apparatus and method for well control and monitoring including an independent web server computer integrated with a pump controller located at each well in an oil field. The well controller locally controls the well pump, processes well and pump data, generates surface and downhole cards, and communicates production reports, recommendations for production improvements, and production statistics to remote sites via the Internet. The controller can be queried remotely to provide production reports, etc. Furthermore, the controller can initiate alerts via email, text messaging, or internet messaging, for example, during fault conditions.”
The '910 Tubel UK Patent discloses:
“A method for controlling a remotely located wellbore tool 29 between modes of operation comprises securing to the wellbore conduit string 13 the electrically actuatable wellbore tool 29, an acoustic sensor 25 and a digital circuit for examining the sensor output to produce a control signal to actuate the tool 29 if it detects that a sensed acoustic signal from a transmitter at the surface has a frequency which has been assigned specifically to the relevant tool. The acoustic transmission comprises pressure pulses passing down a column 55 of wellbore fluid and has a frequency assigned before lowering the string 13 into position in the wellbore. Each tool has one or more assigned frequencies which are programmed into the digital receiver circuit by an operator, using a handset.”
The '911 Tubel UK Patent discloses:
“A method of communicating in a wellbore between a transmission node 45 and a reception node 47, through a fluid column 55 extending there between, comprises the method steps of providing a transmission apparatus 51 at said transmission node which is in communication with said fluid column, and providing a reception apparatus 53 at said reception which includes: (a) a sensor 25 which detects acoustic pulses, and (b) an electronic circuit which examines said acoustic pulses one at a time to determine whether or not they correspond to at least one predefined actuation frequency. The reception apparatus (FIG. 9 not shown) is used to monitor said acoustic transmission during predefined reception intervals associated with said at least one predefined actuation frequency to (1) provide an actuation signal if said acoustic transmission is determined to correspond to said at least one actuation frequency and (2) reset said electronic circuit if said acoustic transmission is determined to define some frequency other than said at least one predefined actuation frequency.”
The Japanese WIPO patent discloses:
“The invention relates to a pumping unit comprising: a base (1) and a rack (2); an electric motor (17) varying frequency power for the pumping unit through a speed reducer (5); a driving hub (7A) connector said speed reducer (5) for driving a belt (10A) and the other belt (11) with one end connected with a balance weight box; a driven hub (7B) connected to said driving hub (7A) for driving a belt (10B) with one end attached to a sucker rod; an upper platform (3) in which said electric motor (17), said speed reducer (5), said driving hub (7A) said driven hub (7B) installed; a driving frequency converter (18) connected with a programmable controller (20) that is connected with an absolute value encoder (16) for dealing with running conditions of the pump unit. The pumping unit can be automatically controlled by the programmable controller with energy conversation, high efficiency and durability.”
An example of an attempt to optimize the performance of an artificial lift system is taught in U.S. Pat. Nos. 5,941,305 and 6,041,856 Thrasher et al. These patents teach a control system of a typical progressive cavity pump, also known as a PCP. A PCP is a corkscrew fixed displacement downhole pump submersed in the well bore, driven by a surface mounted rotary drive, for example an electric motor. The surface mounted drive transfers torque to the rotor of the downhole PCP via sucker rods, “threading” up the well fluids. The fluid flow rate of the PCP is determined, among other parameters, by the speed that the surface mounted drive rotates the downhole pump's rotor. A plurality of sensors and load cells collect data from the well, the pump and the drive and feeds it to a PLC, where the data is compiled to provide an optimal speed command signal to the drive. The scope of the Thrasher inventions is centered on rotary corkscrew downhole pumps and the optimization of their performance via control of their rotational speed. Further, with respect to the monitoring and control system, only the speed of the motor is controlled. Although this concept teaches how to optimize artificial lift production, it is limited to rotary lifting technique, therefore it cannot be applied to the linear reciprocating lifting technique that is part of this invention, neither can it be applied to the broad range of functional and performance parameters that this invention enables to optimize. In addition, the pump and the control system disclosed in the Thrasher patents are subjected to premature failure of the downhole pump due to lack of lubrication and overheating when operating in gassy wells. They are also subjected to premature failure when operating in sandy wells due to surface erosion and damage by the abrasive sand contents in the fluid.